1. Field of the Invention
The present invention relates to a basic flux cored wire with excellent weldability, and more particularly, to a basic flux cored wire, which exhibits excellent crack resistance and low temperature toughness, and is improved in welding workability.
2. Description of the Related Art
Some conventional basic flux cored wires for gas shielded arc welding have excellent crack resistance and low temperature toughness, but are more or less poor in bead appearance and shape, slag removal property and arc stability. These are the disadvantages of basic flux cored wires, compared with titania based flux cored wires. By way of example of conventional non-titania based flux cored wires, a barium fluoride based flux to which Mn, Si, Ni, etc. are added, is disclosed in the Japanese Patent Application Laid-Open Publication No. 62-166098. The barium fluoride based flux cored wire is excellent in low temperature toughness, but welding workability is poor and bead appearance and shape are inferior. With reference to the non-titania based flux cored wire presented in the Japanese Patent Application Laid-Open Publication No. 52-65736, a flux contains Ni, Cu and Mn and the welded structure is heat treated after welding so as to remove residual stress and improve low temperature toughness. However, there are limitations to the improvement of brittle fracture characteristics and low temperature toughness using.
In addition, conventional basic flux cored wires must use a mixed gas (75 to 80% Ar+20 to 25% CO2) as a shield gas in order to secure arc stability and the transfer of metal droplets. Therefore, the basic flux cored wires have a limited applicability.
Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a basic flux cored wire, which is excellent in crack resistance, low temperature toughness and weldability and can use an Ar/CO2 mixed gas or 100% CO2 as a shield gas.
In accordance with the present invention, the above object can be accomplished by the provision of a basic flux cored wire having a mild steel or an alloy steel sheath filled with flux, characterized in that the flux essentially comprise of, with respect to the total weight of the wire:
0.3 to 3.0% Ti and Ti oxide (TiO2-converted value);
1.0 to 2.5% Si and Si oxide (SiO2-converted value);
0.1 to 1.5% Mg and Mg oxide (MgO-converted value);
1.5 to 4.0% Mn and Mn oxide (MnO-converted value);
0.2 to 1.5% Al and Al oxide (Al2O3-converted value);
0.1 to 1.0% Zr and Zr oxide (ZrO2-converted value);
0.2 to 3.5% CaF2; and
0.01 to 0.5% K2O, with the proviso that the components satisfy the basicity(B) of 0.5 to 4.5 in the basicity equation (1) defined as B=(CaF2+MgO+MnO+K2O)/(TiO2+SiO2+Al2O3+ZrO2).